Toward a highly sensitive polymer waveguide fiber Fabry-Pérot ultrasound detector.

In recent times, there has been extensive research on fiber-optic imaging devices in order to enable imaging/sensing at a size scale inaccessible to other modalities. The design for fabrication of a highly sensitive fiber-optic ultrasound detector is proposed. The transducer employs a polymer Fabry-Pérot resonator for ultrasound detection. To enhance acoustic sensitivity, a method is proposed for fabricating a self-aligned polymer waveguide within the cavity to improve the resonator quality factor (Q-factor). Simulation studies were conducted to evaluate feasibility and quantify the improvement in Q-factor for different transducer configurations. Results show that with dielectric mirrors and a waveguide, Q-factor can approach the order of 10,000. Additional simulation studies are presented to analyze the effect of cavity shape on the device performance, drawing out the importance of a flat mirror for waveguided devices. Subsequently, results from optical testing of the first iteration of fabricated devices are presented, highlighting the main drawback of this method-the nonideal shape of the waveguiding pillar. Finally, initial results from the second iteration of devices that overcome this drawback are presented, demonstrating the feasibility of creating straight self-aligned polymer waveguides on gold-coated fibers, followed by a discussion on the implications of this work and future steps.